We propose to conduct an historical cohort study to determine the risks of breast and gynecologic cancers associated with exposure to diethylstilbestrol (DES) during pregnancy. This is a collaborative investigation to be conducted at four study centers and with a central data coordinating center. Study collaborators are participants in the DESAD Project which is an ongoing observational study of women exposed in utero to DES. We anticipate a total cohort of 3,000 mothers exposed during prengnancy mainly in the early 1950's and whose exposure has been ascertained in the DESAD Project by review of obstetric records. In addition, we shall obtain a control cohort of 3,000 unexposed mothers matched to the exposed by age and date of pregnancy. Exposed and control mothers will be contacted by mail and telephone to provide information on health history, hormone usage and other known risk factors for the cancers of concern. For all suspected cancers of interest, clinical details and pathology slides will be sought from medical sources and reviewed centrally according to a uniform protocol. We calculate that with a cohort of 3,000 each of exposed and unexposed mothers we shall have reasonable power (1 - beta equals .90) of detecting a population relative risk of 1.5 for breast cancer and 1.6 for gynecologic cancers.